1. Field of the Disclosure
The present disclosure relates to a method and apparatus for acquiring data in a seismic-while-drilling operation and in particular to transferring data from a downhole location to a surface location.
2. Description of the Related Art
Conventional reflection seismology uses sources and receivers at a surface location and images subsurface layers from reflected seismic energy caused by contrasts in subsurface impedance. An obtained image often suffers in spatial accuracy, resolution and coherence due to the long travel paths between source, reflector, and receiver. In particular, due to the two-way passage of seismic signals with a low, laterally varying velocity through a highly absorptive near-surface weathered layer, subsurface images are often of poor quality.
One technique for overcoming these difficulties is commonly known as vertical seismic profiling (VSP) and images a subsurface in the vicinity of a borehole. VSP measurements made during drilling operations are referred to as Seismic-while-drilling (SWD). In standard SWD exploration, a set of sensors is integrated into a bottomhole assembly (BHA) and lowered into a borehole. The sensors record seismic data from the earth formation in response to seismic energy generated at a surface location. With VSP, a surface seismic source produces signals that are received at a downhole receiver or an array of downhole receivers. This is repeated for different depths of the receiver (or receiver array).
When running a VSP operation, although data is acquired downhole, calculations using the data are generally performed uphole, so that the speed at which data is transferred from the bottomhole assembly to the surface becomes important. In one method, the seismic data is stored at the bottomhole sensor and obtained when the BHA is tripped to the surface. This method suffers from long delays while the BHA is lowered and raised and data is being collected. Alternatively, mud pulse telemetry in which uncoded acoustic signals are produced at the BHA and received at the surface makes it possible for a surface operator to obtain data without removing the sensor from its downhole location and continued collecting data. However, the rate at which data is sent uphole using telemetry is limiting, especially when compared to the large amount of data that typically needs to be sent uphole. Thus, there is a need for improving the speed at which data is communicated uphole in VSP methods.